Air streams which are introduced at different temperature levels through a common duct in heating, ventilating and air conditioning (HVAC) systems require intimate mixing in the duct in order to avoid undesirable stratification of air prior to passage of the airstream into a room airspace to be heated or cooled. Failure to achieve intimate mixing in the duct ultimately results in inefficient heating and cooling of the room air space and therefore can significantly affect the cost in operating and maintaining an HVAC system.
A number of prior art references exist which disclose various static air mixing devices. The assignee of the current invention is the owner of a number of previous patents to include U.S. Pat. Nos. 3,180,245; 4,495,858; 5,645,481; and 5,536,207. Each of these references are hereby incorporated by reference for teaching the basic air mixing apparatuses disclosed therein.
An air mixing device installed in an air duct inherently creates a pressure drop in the airflow across the air mixer during operation.- This pressure drop is undesirable and therefore, efforts to minimize pressure drop is a main consideration in static air mixing design. Of course, it is also desirable to maximize the efficiency of the mixing that takes place immediately downstream of the mixing apparatus as well as to maintain a uniform velocity profile downstream of the mixing device.
Earlier mixer designs typically had mixing efficiencies of around 30%. In later mixer designs, mixing effectiveness has been greatly improved, and it is not uncommon to find mixers with efficiencies of around 50 or 60%. With the optimized construction of the air mixers disclosed in the U.S. Pat. Nos. 5,645,481 and 5,536,207, air mixing effectiveness of at least 65% was achieved.
Although mixing efficiency has improved due to newer mixer designs, one drawback from some of the newer mixer designs is the complexity of the air mixers, and the cost to manufacture such units.
Therefore, there is a need for development of yet a different mixer design which still achieves acceptable mixer effectiveness, but is of a simpler design which reduces manufacturing costs and makes the mixer more available for all types of commercial use.